DNA methyltransferase 1 (DNMT1) is an essential regulator maintaining both epigenetic reprogramming during DNA replication and genome stability. We investigated the role of DNMT1 in the regulation of postnatal liver histogenesis under homeostasis and stress conditions. We generated Dnmt1 conditional knockout mice (Dnmt1(Δalb) ) by crossing Dnmt1(fl/fl) with Albumin-Cre (Alb-Cre) transgenic mice. Serum, liver tissues and primary hepatocytes were collected from 1-20 week old mice. The Dnmt1(Δalb) phenotype was assessed by histology, confocal and electron microscopy, biochemistry as well as transcriptome and methylation profiling. Regenerative growth was induced by partial hepatectomy and exposure to CCl4 . The impact of Dnmt1 knockdown was also analyzed in hepatic progenitor cell (HPC) lines; proliferation, apoptosis, DNA damage and sphere formation were assessed. Dnmt1 loss in postnatal hepatocytes caused global hypomethylation, enhanced DNA damage response and initiated a senescence state causing a progressive inability to maintain tissue homeostasis and proliferate in response to injury. The liver regenerated via activation and repopulation from progenitors due to lineage-dependent differences in Alb-Cre expression, providing a basis for selection of less mature and therefore less damaged HPC progeny. Consistently, an efficient knockdown of Dnmt1 in cultured HPCs caused severe DNA damage, cell cycle arrest, senescence and cell death. Mx1-Cre-driven deletion of Dnmt1 in adult quiescent hepatocytes did not affect liver homeostasis.

CONCLUSION: These results establish the indispensable role of DNMT1-mediated epigenetic regulation in postnatal liver growth and regeneration. The Dnmt1(Δalb) mice provide a unique experimental model to study the role of senescence and contribution of progenitor cells to physiological and regenerative liver growth. This article is protected by copyright. All rights reserved.